CSCI 370 - View Groups and Layouts

views

basic building blocks of an android graphical user interface, object that knows how to draw itself on the screen, responsible for a rectangular area on the screen and for handling events in that area

Widget

an object that interacts directly with the user (e.g., button or check box)

ViewGroup

a view that acts as a container to hold its children

Layout

a ViewGroup that is responsible for positioning its children on the screen

XML filles for layout

must contain exaclty one root element, is placed in the res/layout or the res/layout-land, compiled into a View resource

Attributes

can be inherited by View classes, some are specific to a view object

id attribute

used to uniquely identify the View within the tree

LinearLayout

displays its child View elements in a linear direction, either vertically or horizontally, creates a scrollbar if the length of the window exceeds the length of the screen

ConstraintLayout

allows you to create large and complex layouts with a flat view hierarchy (i.e., no nested view groups)

TableLayout

ViewGroup that displays its child View elements in rows and columns to HTML
tables, will have as many columns as the row with the most cell

Child views of tableLayout

TableRow objects

stretchable column

can expand in width to fit any extra space

shrinkable column

can be shrunk to fit the table into its parent object.

RecyclerView

view group that displays a list of scrollable items, the layout involves two XML files, is not a layout but is usually the only view within a parent layout